Estimation of heat losses due to wind effects from linear parabolic secondary reflector –receiver of solar LFR module

Abstract

A numerical study is carried out to determine the heat losses caused by natural and forced convection as well as radiation from the parabolic secondary receiver of a Solar Linear Fresnel Reflector system. The geometric configuration considered corresponds to an absorber tube placed in an open aperture. Thermal performance of the receiver with the acceptance angle θa= 45°, truncation point H/W = 0.6, focal position of the absorber f= 7.9 m and gap between the secondary reflector and absorber tube (G) to the height of the secondary reflector (H) at G/H = 0.14 are considered for the thermal analysis. Thermal losses from the reflector over a wide range of temperature(373K−773K), diameter ratio (0.14−0.27) and emissivity (0.01−1) are analysed. Realistic conditions including the effects of wind and commerically available absorber diameter and emissivity values are considered to assess the performance of the receiver. Investigation is carried out to determine the heat losses at wind velocities up to 10 m/s. Nusselt number correlations are proposed for determining the heat losses from a solar cavity open aperture with CPC profile. The proposed correlations are functions of the temperature ratio(Th/T∞) , diameter ratio, emissivity, Grashof number and Reynolds number and they are very useful for predicting the heat losses from the linear receiver of a typical solar LFR system.